Coastal cities and cities which are located on river banks are commonly afflicted with severe and sometimes dangerous concentrations of heavy metals, including copper, iron and lead in the sediments of the adjacent water bodies. These metals often have deleterious effects on the local population of fish and other aquatic life, resulting in death, malformation or failure to reproduce. In areas where people fish or harvest other types of sea life for food, the high concentrations of metals in the animals' bodies is passed on to the individuals who consume them, endangering their health.
In some cases, the metal contaminants are introduced during the transfer of metal ore between transport vessels and a loading dock. In other instances, contaminants have been released during a variety of vessel maintenance activities, including, among others, metal refinishing or cleansing. Thus, the metal contaminants can have a particularly high concentration within a relatively limited area, creating a "hot spot". Because of tidal activities, these hot spots can diffuse over wide areas, resulting in decreasing contamination gradients over these zones.
The typical procedure for mitigating these above-background concentration areas is to dredge the contaminated area, removing the sediment to a landfill or other disposal site. This increases the burden on the limited available landfill space, and, even more importantly, does not address the long term issue of toxicity. Instead, it merely shifts the contaminant to an area where it may cause less environmental harm on a short term basis. In the alternative, the entirety of the dredged material can be chemically treated to remove the contaminant. While effective at removing the contaminant, this process is prohibitively time consuming and expensive. As is often the case, the economic issues are the determining factor and, until now, there has been no process available which could satisfy both the economic and ecological issues involved in removal of metal contaminants from sediment in bays, harbors, lakes and rivers.